Plastic material is now common in everyday life, and ultimately, when used as a disposable product, plastic has also found itself as a significant contributor to the problem of solid waste management. With respect to solid waste management, several different options have been identified to date to deal with the ever increasing need to conserve the valuable and non-renewal resources associated with plastic material production and disposal. For example, "source reduction" which refers to a reduction in the amount of material that is used in any application, and, therefore, a reduction in the amount of material potentially discarded when that use is completed.
However, recycling remains a much more environmentally favored route over "source reduction", and is based upon the reprocessing and refabrication of a plastic material that has been used and discarded by the consumer which otherwise would be destined for disposal. This type of recycling has now become well known as post-consumer recycling (PCR), as opposed to recycling that develops as part of the reuse of by-products from a plastic manufacturing process (which by-products are generally known as "regrind").
Unfortunately, the reprocessing and refabrication of PCR materials into useful products requires several steps (collection, handling/sorting, reclamation/cleaning and end-use fabrication) and presents unique problems. That is, each of these steps has remained relatively expensive, not the least of which is the requirement to insure that the recycled plastic material at issue is clean and safe for consumer reuse. In that regard, it is an altogether simple matter to envision that while in the hands of consumers, intentionally or otherwise, plastic materials can and will come into contact with other more toxic chemicals, and as plastic materials can absorb such toxins, this requires cleaning and detection (of any residual toxins) prior to placement of such material back into the consumer's hands. Of course, this is even more the case to the extent that the recycled material is targeted for an application involving direct food or beverage contact.
Not surprisingly therefore, and to assure consumer safety, regulatory agencies promptly became active with respect to the use of PCR material for food/beverage applications. For example, in 1992 the Food and Drug Administration published proposed guidelines for recycling, which divided plastics recycling into three classes: Primary recycling of plastics which are plant scrap without any consumer exposure; Secondary recycling involving the physical cleaning of post-consumer plastics by physical processes such as washing, vacuum and heat treatment; and Tertiary recycling involving chemical treatment, usually depolymerization (breaking the plastic material down into its building blocks, known as "monomers"), followed by monomer purification and reconstitution back to plastic material. See, "Points to Consider for the Use of Recycled Plastics in Food Packaging: Chemistry Considerations", U.S. FDA, Center for Food Safety and Applied Nutrition (HFS-245), Washington, D.C. April 1992.
With regards to secondary recycling, it should now be apparent that central to any efficient physical cleaning operation is the need to monitor the washing procedures to determine whether or not any recycled plastic material at issue is void of residual contaminant, or whether or not the residual contaminant is present at a level such that it would not migrate out when placed in contact with a food/beverage media. For further discussion see, e.g., "The Threshold of Regulation and its Application to Indirect Food Additive Contaminants in Recycled Plastics", Food Additives and Contaminants", 1997, Vol. 14, No. 6-7, 661-670.
Toward such monitoring objectives, a variety of U.S. Patents have been issued directed at sampling and determining the presence of contaminants in recyclable plastic materials, which for the most part have been based upon the well-known analytical tool known as gas chromatographic (GC) instrumentation. Chromatography provides timewise separation of gases or liquid samples as part of analyses in which specific compounds are detected. This timewise separation achieved among constituents permits particular compounds to be distinguished from interferents and from other specific compounds of interest by signal peaks which occur at distinct times at the output of detectors downstream of the chromatograph. The times at which the detector "detects" a given constituent, as well as the amplitude and shape can be predetermined by calibration techniques using samples of known composition, and detection systems containing the chromatographs can be electronically programmed to provide alarms or specific responses upon detection of each compound of interest.
For example, in U.S. Pat. No. 5,073,203, entitled "Method for Recycling Polyethylene Terephthalate (PET) Beverage Bottles by Treating with Carbon Dioxide", there is disclosed a method for recycling polymer materials based on PET used for food packaging such as beverage bottles. As disclosed therein, when such PET resin, in the form of crushed bottles, is washed/extracted by a fluid such as supercritical CO.sub.2, at preferred temperatures between 31.degree. and 245.degree. C., the contaminants therein are removed, without any effect on the PET intrinsic viscosity. The washed PET is then tested by GC equipment, and the GC tests therein indicated that under such conditions the contaminant material had been successfully removed.
Attention is also directed to U.S. Pat. Nos. 4,830,192, 4,858,768 and 5,067,616 which describes a method of discriminating between contaminated and uncontaminated containers prior to washing by testing the residue of the container to determine if the residue is the residue of the original product in the container. If the residue is not sufficiently similar to the original product, the container is rejected as contaminated.
Other related disclosures of interest include U.S. Pat. No. 5,108,705, which discloses a method and apparatus for high speed, selective detection of vapors of specific compounds, utilizing a bypass branch and high speed gas chromatography for improved selectivity and detection. In U.S. Pat. No. 4,843,016 a detection system is disclosed for detecting the presence of predetermined compounds in a sample. This system similarly comprises a sample injector, a chromatographic column, a conversion means and one or more specific gas detectors. The conversion means is said to transform the column effluent to combustion products in the gas phase, after which those combustion products are transferred to the specific gas detectors.
In U.S. Pat. No. 4,880,120, entitled "Plastic Container Inspection Process", there is disclosed a container inspection process for detecting the presence of contaminants in plastic containers. More specifically, the process flushes volatiles from within the container by injecting gas, draws a vapor sample from within the container and analyzes the sample by ionization techniques.
In U.S. Pat. No. 5,352,611 there is disclosed a method and apparatus for samples and determining the presence of residues of contaminants in containers. The method includes the steps of injecting a fluid described as air or CO.sub.2 into the containers in order to displace a portion of the contents, evacuating a sample of the container contents so displaced by applying suction thereto, and analyzing the sample evacuated to determine the presence or absence of any residues therein.
Accordingly, while various efforts have been made for monitoring contaminants in recycled material, as the above discussion has shown, many of these techniques in one form or another focus on the sampling of contaminant from an individual contaminated container, which is an uncooperative requirement as applied to the goal of developing a fast and efficient recycling operation with continuous output. That is, sampling each and every individual container collected and ultimately reprocessed through a recycling facility is time-consuming and economically unattractive, particularly as the need for high-speed recycling grows in the marketplace.
Furthermore, in the case of previous attempts to monitor contaminants in recycled ground flake, as opposed to the container itself in a given recycling facility, to date there have been no reports wherein such procedure is efficiently coordinated with an in-plant continuous method for discriminating between levels of contamination derived from a given population of, e.g. PET containers. In other words, to the extent that PCR-PET flake has been analyzed for contaminants, it has been largely demonstrated on isolated portions of the flake, and not itself coupled to an in-plant continuous quality control system to satisfy, e.g., the strict requirements discussed above set by the FDA for the preparation of food grade packages made from recycled material.
Stated another way, none of the techniques disclosed to date have developed a method to continuously trigger a more reliable concentration of contaminants per unit of air space (above contaminated flake material) which in turn would provide far greater and more reliable detection capability. And towards such end, the prior art has also yet to develop a technique whereby one ensures that ejected volatile contaminant gases remain substantially within the air spaces between a relatively large sample of flake so that such contaminants can themselves be delivered to a detection station removed from that location where the contaminant gases are first made to migrate out of a given sample.
Furthermore, none of the prior art disclosures to date have coordinated and assimilated detection information/data into a tracking data management center which is configured in active communication and coordinates control of a recycling plant's processing of recycled material such that said tracking data management center can signal, divert and/or isolate contaminated recycled material from non-contaminated material when said recycled material exceeds preselected contamination levels. Nor has the prior art recognized the utility and advantage of coordinating the monitoring and control of contaminated flake to the extent that such monitoring and control is applied both to incoming and so-called "dirty" flake, and to flake that has been processed (i.e., "cleaned") through a recycling plant facility.
Therefore, it is a primary object of the present invention to provide a method and system for the monitoring and control of contaminants in a specific portion of the production of shredded, pelletized or flaked plastic materials. More specifically it is a primary object of the present invention to continuously monitor and detect the presence of trapped volatile contaminant substances in a recycled plastic material as the recycled material is selectively sampled from a main recycling production line facility, to deliver such monitoring information to a programmable logic controller (PLC) which is programmed to both identify and signal at a preselected contaminant levels, as well as acting to divert and isolate PCR plastic containing said selected and detected contaminant level from plastic material which contains an acceptable threshold of contaminants.
Accordingly, it is an object of the present invention to provide a unique and overall QC system for continuous sampling, monitoring and detection of contaminants in recycled plastic materials, including both dirty and clean flake, and to coordinate such system directly with in-plant process control, wherein the recycled plastic material is specifically recycled PET.